The present invention relates to a water pump, and more particularly to a variable-capacity water pump having an impeller construction capable of varying the capacity of the water pump.
Systems for cooling automotive engines have heretofore incorporated a water pump, as shown in FIG. 1 of the accompanying drawings, which is driven by the engine for forcibly circulating cooling water to cool the cylinder block and head. The water pump, generally designated at 10, has a rotatable shaft 11 drivable by the automotive engine and a pump impeller 12 fixed to an end of the rotatable shaft 11 which extends into a cooling water inlet tube 16. The pump impeller 12 has a boss 12a secured to the rotatable shaft 11, a flange 12b extending radially outwardly from the boss 12a, and impeller vanes 12c integrally projecting axially from the flange 12b. The water pump 10 also includes a mechanical seal 14 disposed behind the pump impeller 12 and normally urged by a spring 13 for preventing cooling water from leaking into a driving unit 15 on the rotatable shaft 11.
It is preferable that the quantity of cooling water flowing in such an engine cooling system be small during the warming-up of the engine or in the normal running condition. With the foregoing prior water pump, the pump impeller operates fully in response to rotation of the shaft 11, and will have already reached its full operation capacity when the engine is to be cooled. Accordingly, the water pump causes an increased power loss, and suffers from a poor cooling efficiency.
There has been proposed an engine cooling device, as disclosed in Japanese Laid-Open Patent Publication No. 51-98447, for reducing the quantity of cooling water flowing in the warming-up of the engine and normal running condition. The discosed engine cooling device has a control valve disposed in a cooling water passage for varying the quantity of cooling water to be supplied to a water pump dependent on the temperature of the cooling water. Since the cooling water flows into the control valve under a prescribed pressure, an arrangement is required to allow the control valve to operate reliably without being adversely affected by the water pressure acting on the control valve. In addition, the overall construction is complex because an attachment is needed for mounting the control valve and a space should be reserved in the cooling water passage for placing the control valve therein.